Process for preparing fluoropolymer

ABSTRACT

The polymerization initiator-containing solution of the first invention is obtained by mixing a specific perfluorodicarboxylic acid fluoride (A) with CsF in an aprotic polar solvent with stirring to conduct reaction and thereby form a polymerization initiator (B) and then allowing the reaction solution to stand for not less than 72 hours at a temperature of 0 to 30° C. The polymerization initiator-containing solution of the second invention comprises a specific polymerization initiator (B′) and an aprotic polar solvent. The process for preparing a perfluoropolyether according to the invention comprises polymerizing hexafluoropropylene oxide in the presence of the polymerization initiator-containing solution.

FIELD OF THE INVENTION

[0001] The present invention relates to a process for preparing afluoropolymer and a solution catalyst capable of providing afluoropolymer. More particularly, the invention relates to a process forpreparing a perfluoropolyether, comprising polymerizinghexafluoropropylene oxide in a special polymerizationinitiator-containing solution.

BACKGROUND OF THE INVENTION

[0002] Bifunctional perfluoropolyether oligomers can undergocrosslinking reaction or can be made to have high molecular weight bytaking advantage of functional groups present at both ends, andtherefore they are useful as resins for sealants, adhesives andvulcanized rubber molded articles having excellent solvent resistanceand chemical resistance. The bifunctional perfluoropolyethers can befavorably used as resins which are used for, for example, moldedarticles, such as O-ring, gasket, diaphragm and tube, sealing agents ofchemical plant pipes, sealing agents of tank flanges, and adhesives.

[0003] It has been heretofore known that the bifunctionalperfluoropolyether (sometimes referred to as “PFE” hereinafter) isprepared by polymerizing hexafluoropropylene oxide (sometimes referredto as “HFPO” hereinafter) in the presence of an appropriate catalyst orpolymerization initiator.

[0004] In the polymerization of HFPO, chain transfer caused by compoundsother than the polymerization initiator, e.g., chemical species such asH₂O, HF and a carbonyl group, is very liable to take place, so that itis important to eliminate inclusion of the chemical species other thanthe polymerization initiator to the utmost thereby to inhibitpolymerization initiation from such chemical species and to conductpolymerization reaction under the conditions where formation ofby-products such as compounds other than the intended bifunctionalperfluoropolyether can be inhibited. In particular, H₂O is presentanywhere, e.g., in air, and there is a high possibility of inclusion ofH₂O into the polymerization system. Hence, it is very important toeliminate inclusion of H₂O.

[0005] It is known that in order to enhance selectivity of thebifunctional perfluoropolyether, the polymerization reaction needs to bepromoted with maintaining the polymerization temperature of HFPO as lowas possible. It is also known that lowering of the polymerizationtemperature in the polymerization of HFPO not only inhibits chaintransfer but also enhances selectivity of the reaction and degree ofpolymerization of the resulting polymer. Further, it is also known thatuse of the bifunctional initiator as the polymerization initiatorreduces formation of a monofunctional polymer (by-product).

[0006] In “J. MACROMOL. SCI. —CHEM.”, 48(3), 499-520 (1974), there isdescribed a process wherein hexafluoropropene (sometimes referred to as“HFP” hereinafter) is allowed to be present during the polymerization ofHFPO to inhibit chain transfer and to increase degree of polymerizationof the resulting polymer.

[0007] In U.S. Pat. No. 3,660,315 and Japanese Patent Publication No.5360/1978, there is described a process for preparing a bifunctionalperfluoropolyether, comprising mixing cesium fluoride, tetraglyme andFOCCF(CF₃)OCF₂CF₂OCF(CF₃)COF with one another and allowing HFPO toreact, at a low temperature, with a compound of the following formulacontained in the resulting homogenous solution from which extra cesiumfluoride has been separated.

[0008] The present inventors have made an attempt to synthesize acompound represented by the above formula and to prepare a bifunctionalperfluoropolyether from HFPO in the presence of the resulting compound,in accordance with the process described in U.S. Pat. No. 3,660,315 andJapanese Patent Publication No. 5360/1978. As shown in ComparativeExample 1 or 2 in this specification, however, when the degree of agingof the catalyst or the concentration of the catalyst is out of a certainrange, the degree of polymerization and the selectivity of thebifunctional perfluoropolyether are lowered, resulting in lack ofutility.

[0009] In Japanese Patent Laid-Open Publication No. 101788/1998, thereis described a process for preparing a bifunctional polyether, whereinin order to increase selectivity of the reaction, heat of polymerizationis removed from the highly viscous HFPO polymerization system to lowerthe polymerization temperature, and in order to inhibit chain transfer,a liquefied gas of fluorocarbon of 1 to 4 carbon atoms is added to thereaction system and HFPO is polymerized with evaporating the liquefiedgas from the polymerization system. In this process, however, absence ofextra HFPO is necessary for inhibition of side reaction such asformation of a monofunctional product, and it is sometimes difficult tocontrol the reaction.

[0010] It is difficult to completely remove a chain transfer-causingcompound, such as H₂O, HF or a carbonyl group-containing compound, fromHFPO that is a starting material of a perfluoropolyether. Accordingly,there has been desired development of a process for preparing abifunctional perfluoropolyether wherein even if such a chaintransfer-causing compound is present in a trace amount, a bifunctionalperfluoropolyether can be readily obtained with high degree ofpolymerization and high selectivity.

[0011] Under such circumstances, the present inventors have earnestlystudied in order to solve the above problems. As a result, they havefound that when a polymerization initiator-containing solution havingbeen subjected to a certain treatment is used as a polymerizationcatalyst, a bifunctional perfluoropolyether can be obtained with highdegree of polymerization and high selectivity. The present inventorshave also found that this polymerization initiator-containing solutionis in a liquid state even at low temperatures. Based on the finding, thefirst invention has been accomplished.

[0012] Moreover, the present inventors have found that when apolymerization initiator-containing solution which contains no freeCs⁺F⁻ is used as a polymerization catalyst, a bifunctionalperfluoropolyether can be obtained with high degree of polymerizationand high selectivity. The present inventors have also found that thispolymerization initiator-containing solution is in a liquid state evenat low temperatures. Based on the finding, the second invention has beenaccomplished.

OBJECT OF THE INVENTION

[0013] It is an object of the present invention to provide a convenientprocess for preparing a bifunctional perfluoropolyether with high degreeof polymerization and high selectivity. In particular, it is an objectof the first invention to provide a solution catalyst which serves as apolymerization catalyst, can be in a liquid state even at a lowtemperature during the polymerization reaction, can be homogeneouslydispersed in the polymerization reaction system and exhibits low chaintransfer property and high activity.

SUMMARY OF THE INVENTION

[0014] The summary of the present invention is described below.

[0015] The polymerization initiator-containing solution according to theinvention is a polymerization initiator-containing solution capable ofbeing obtained by mixing a perfluorodicarboxylic acid fluoride (A)represented by the following formula (I) with CsF in an aprotic polarsolvent with stirring to conduct reaction and thereby form apolymerization initiator (B) and then allowing the reaction solution tostand for not less than 72 hours at a temperature of 0 to 30° C.;

FOC—Rf—COF  (I)

[0016] wherein Rf is a perfluoroalkylene group having 1 to 4 carbonatoms or a perfluoroalkylene group having 2 to 10 carbon atoms and anether bond.

[0017] The process for preparing a polymerization initiator-containingsolution according to the invention comprises mixing aperfluorodicarboxylic acid fluoride (A) represented by the followingformula (I) with CsF in an aprotic polar solvent with stirring toconduct reaction and thereby form a polymerization initiator (B) andthen allowing the reaction solution to stand for not less than 72 hoursat a temperature of 0 to 30° C.;

FOC—Rf—COF  (I)

[0018] wherein Rf is a perfluoroalkylene group having 1 to 4 carbonatoms or a perfluoroalkylene group having 2 to 10 carbon atoms and anether bond.

[0019] The process for preparing a perfluoropolyether according to theinvention comprises polymerizing hexafluoropropylene oxide in thepresence of the above-mentioned polymerization initiator-containingsolution.

[0020] The polymerization initiator (B) contained in the polymerizationinitiator-containing solution is preferably a compound represented bythe following formula (II):

CsOCF₂—Rf—CF₂OCs  (II)

[0021] wherein Rf is a perfluoroalkylene group having 1 to 4 carbonatoms or a perfluoroalkylene group having 2 to 10 carbon atoms and anether bond.

[0022] The concentration of the polymerization initiator (B) in thepolymerization initiator-containing solution is preferably not less than4×10⁻⁴ mol/g.

[0023] The polymerization of the hexafluoropropylene oxide is preferablycarried out at a temperature of not higher than −30° C.

[0024] In the polymerization of the hexafluoropropylene oxide, it ispreferable to further use hexafluoropropylene in combination in anamount of 20 to 50% by weight based on the amount of thehexafluoropropylene oxide.

[0025] The perfluorodicarboxylic acid fluoride (A) is preferablyrepresented by the following formula (III):

[0026] wherein Rf¹ is a perfluoroalkylene group having 2 to 4 carbonatoms.

[0027] The aprotic polar solvent is preferably diglyme, triglyme,tetraglyme or sulfolane.

[0028] The process for preparing a perfluoropolyether according to theinvention comprises polymerizing hexafluoropropylene oxide in thepresence of a polymerization initiator-containing solution whichcomprises a polymerization initiator (B′) represented by the followingformula (IV) and an aprotic polar solvent;

(FOC)_(x)—Rf²—(CF₂OCs)_(y)  (IV)

[0029] wherein Rf² is perfluoroalkylene having 1 to 4 carbon atoms orperfluoroalkylene having 2 to 10 carbon atoms and an ether bond, and xand y are numbers satisfying the conditions of x+y=2 and 0.1<y<2.

[0030] Rf² in the formula (IV) is preferably represented by thefollowing formula (V):

[0031] wherein Rf³ is perfluoroalkylene having 2 to 6 carbon atoms.

[0032] The polymerization of the hexafluoropropylene oxide is preferablycarried out at a temperature of not higher than −30° C.

[0033] The concentration of the polymerization initiator (B′) in thepolymerization initiator-containing solution is preferably not less than4×10⁻⁴ mol/g.

[0034] In the polymerization of the hexafluoropropylene oxide,hexafluoropropylene can be further used in combination in an amount of20 to 50% by weight based on the amount of the hexafluoropropyleneoxide.

[0035] The polymerization initiator (B′) is preferably a compoundobtained by allowing a perfluorodicarboxylic acid fluoride (A′)represented by the following formula (VI) to react with CsF in anaprotic polar solvent;

FOC—Rf⁴—COF  (VI)

[0036] wherein Rf⁴ is a perfluoroalkylene group having 1 to 4 carbonatoms or a perfluoroalkylene group having 2 to 10 carbon atoms and anether bond.

[0037] The perfluorodicarboxylic acid fluoride (A′) is preferablyrepresented by the following formula (VII):

[0038] wherein Rf⁵ is a perfluoroalkylene group having 2 to 4 carbonatoms.

[0039] The molar ratio (CsF/perfluorodicarboxylic acid fluoride (A′)) ofthe CsF to the perfluorodicarboxylic acid fluoride (A′) used ispreferably not less than 0.1 and less than 2.

[0040] The aprotic polar solvent is preferably diglyme, triglyme,tetraglyme or sulfolane.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIG. 1 shows changes in a ¹⁹F-NMR spectrum of a fluorine atom of—CF₂OCs at the end of a polymerization initiator (B) and an integralvalue of the fluorine atom with time, said polymerization initiator (B)being represented by the following formula (II) and obtained by mixing aperfluorodicarboxylic acid fluoride (A) represented by the followingformula (I) with CsF in an aprotic polar solvent with stirring;

FOC—Rf—COF  (I)

[0042] wherein Rf is a perfluoroalkylene group having 1 to 4 carbonatoms or a perfluoroalkylene group having 2 to 10 carbon atoms and anether bond;

CsOCF₂—Rf—CF₂OCs  (II)

[0043] wherein Rf is the same as Rf in the formula (I)

[0044] FIGS. 1(a), 1(b), 1(c) and 1(d) show ¹⁹F-NMR spectra and integralvalues of the above fluorine atom measured after a lapse of 24 hours, 48hours, 96 hours and 30 days, respectively, from disappearance of thestarting compound represented by the formula (I).

DETAILED DESCRIPTION OF THE INVENTION

[0045] The present invention is described in detail hereinafter.

[0046] In the process for preparing a perfluoropolyether according tothe invention, hexafluoropropylene oxide is polymerized in the presenceof a special polymerization initiator-containing solution to prepare aperfluoropolyether. First, the polymerization initiator-containingsolution is described.

Polymerization Initiator-containing Solution

[0047] The polymerization initiator-containing solution of the firstinvention and the polymerization initiator-containing solution of thesecond invention are described below.

[0048] The polymerization initiator-containing solution of the firstinvention is a solution catalyst which can be obtained by mixing aperfluorodicarboxylic acid fluoride (A) represented by the followingformula (I) with CsF in an aprotic polar solvent with stirring toconduct reaction and thereby form a polymerization initiator (B) andthen allowing the reaction solution to stand for not less than 72 hoursat a temperature of 0 to 30° C.;

FOC—Rf—COF  (I)

[0049] wherein Rf is a perfluoroalkylene group having 1 to 4 carbonatoms or a perfluoroalkylene group having 2 to 10 carbon atoms and anether bond.

[0050] In the formula (I), Rf is a perfluoroalkylene group having 1 to 4carbon atoms or a perfluoroalkylene group having 2 to 10 carbon atomsand an ether bond. Examples of Rf include groups represented by thefollowing formulas:

[0051] wherein n is an integer of 1 to 6.

[0052] Of these, a group represented by the following formula ispreferable in the first invention.

[0053] Of the perfluorodicarboxylic acid fluorides having such groups,particularly preferably used in the first invention is aperfluorodicarboxylic acid fluoride wherein n in the above group is aninteger of 2 to 4, namely, a perfluorodicarboxylic acid fluoriderepresented by the following formula (III):

[0054] wherein Rf¹ is a perfluoroalkylene group having 2 to 4 carbonatoms.

[0055] The polymerization initiator-containing solution of the secondinvention is a solution catalyst obtained by mixing aperfluorodicarboxylic acid fluoride (A′) represented by the followingformula (VI) with CsF in a mixing ratio by mol of 1:0.1 to less than 2.0(perfluorodicarboxylic acid fluoride:CsF) in an aprotic polar solventwith stirring to conduct reaction and thereby form a polymerizationinitiator (B′) represented by the following formula (IV);

FOC—Rf⁴—COF  (VI)

[0056] wherein Rf⁴ is a perfluoroalkylene group having 1 to 4 carbonatoms or a perfluoroalkylene group having 2 to 10 carbon atoms and anether bond;

(FOC)_(x)—Rf²—(CF₂OCs)_(y)  (IV)

[0057] wherein Rf² is perfluoroalkylene having 1 to 4 carbon atoms orperfluoroalkylene having 2 to 10 carbon atoms and an ether bond, and xand y are numbers satisfying the conditions of x+y=2 and 0.1<y<2.

[0058] In the present specification, the polymerization initiatorrepresented by the formula (IV) is a mixture of two kinds ofpolymerization initiators represented by the following formulas (IV-1)and (IV-2):

(CF₂OCs)—Rf²—(CF₂OCs)  (IV-1)

(FOC)—Rf²—(CF₂OCs)  (IV-2)

[0059] wherein Rf² is perfluoroalkylene having 1 to 4 carbon atoms orperfluoroalkylene having 2 to 10 carbon atoms and an ether bond.

[0060] x and y in the formula (IV) indicate proportions of two kinds offunctional groups (—CF₂OCs and —COF) present in the whole polymerizationinitiator, said proportions corresponding to mixing proportions of thepolymerization initiators represented by the formulas (IV-1) and (IV-2)The perfluorodicarboxylic acid fluoride (A′) for use in the secondinvention is represented by the formula (VI), and Rf⁴ in the formula(VI) is a perfluoroalkylene group having 1 to 4 carbon atoms or aperfluoroalkylene group having 2 to 10 carbon atoms and an ether bond.

[0061] Examples of Rf⁴ include groups represented by the followingformulas:

[0062] wherein n is an integer of 1 to 6.

[0063] Of these, a group represented by the following formula ispreferable in the second solution.

[0064] Of the perfluorodicarboxylic acid fluorides having such groups,particularly preferably used in this invention is aperfluorodicarboxylic acid fluoride wherein n in the above group is aninteger of 2 to 4, namely, a perfluorodicarboxylic acid fluoriderepresented by the following formula (VII):

[0065] wherein Rf⁵ is a perfluoroalkylene group having 2 to 4 carbonatoms.

[0066] The aprotic polar solvent for use in the first and the secondinventions is preferably one having a large dielectric constant ε and noproton-donative group. For example, preferable is an aprotic polarsolvent exhibiting marked interaction to the ionic reaction activespecies, because it generally is rich in the association properties andhas large proton variable capacity, and therefore if it is used as asolvent for organic ionic reaction, its self association is loosened toform a more stable salvation state.

[0067] Examples of the aprotic polar solvents includeN,N-dimethylformamide, N,N-dimethylacetamide, tetramethylurea, dimethylsulfoxide, hexamethylphosphoramide, acetonitrile, tetramethylene sulfone(sulfolane), propylene carbonate, nitrobenzene, nitromethane, dimethylcyanamide, tetrahydrofuran, dioxane and pyridine.

[0068] A hydrocarbon compound having at least one ether bond, preferably1 to 3 ether bonds, in a molecule can also be preferably used, andexamples of such compounds include ethyl methyl ether, diethyl ether,monoglyme (ethylene glycol dimethyl ether), diglyme (diethylene glycoldimethyl ether) and tetrahydrofuran.

[0069] Also employable is a chain or cyclic hydrocarbon compound having5 or more ether bonds in a molecule, such as tetraglyme (tetraethyleneglycol dimethyl ether) or crown ether (15-crown-5, 18-crown-6).

[0070] Of the above compounds, monoglyme, diglyme, tetraglyme orsulfolane is preferably used in the invention, and tetraglyme is morepreferably used in the invention.

[0071] Next, the process for preparing a polymerizationinitiator-containing solution according to the invention is described.

Process for Preparing Polymerization Initiator-containing Solution ofthe First Invention

[0072] The polymerization initiator-containing solution of the firstinvention can be obtained by mixing the perfluorodicarboxylic acidfluoride (A), cesium fluoride (CsF) and the aprotic polar solvent withone another with stirring to conduct reaction and thereby form apolymerization initiator (B) and then allowing the reaction solution tostand (aging the solution) for not less than 72 hours, preferably notless than 84 hours, more preferably not less than 96 hours, at atemperature of 0 to 30° C.

[0073] There is no specific limitation on the mixing of theperfluorodicarboxylic acid fluoride (A), cesium fluoride (CsF) and theaprotic polar solvent with stirring. For example, to CsF placed in aflask equipped with a stirrer, a mixed solution of theperfluorodicarboxylic acid fluoride (A) and the aprotic polar solvent isdropwise added with stirring the CsF in the flask. The temperature forthe mixing is not specifically limited and is usually room temperature.

[0074] The starting point of the aging time (72 hours) is a point oftime at which the polymerization initiator (B) is formed by the reactioncaused by mixing the perfluorodicarboxylic acid fluoride (A), cesiumfluoride (CsF) and the aprotic polar solvent with one another withstirring, and is specifically a point of time at which most of the —COFgroups at the ends of molecules of the perfluorodicarboxylic acidfluoride (A) in the solution disappear. Presence of the —COF group atthe molecular end can be confirmed by, for example, partly withdrawing asample containing —COF from a reaction solution that is being stirredand measuring an integral value of F atom of the —COF contained in thesample by means of ¹⁹F-NMR.

[0075] For aging the resulting solution, a method of allowing thesolution to stand still, a method of slowly stirring the solution, amethod of applying ultrasonic wave to the solution or a method ofcombining these methods is available. Of these, the method of allowingthe solution to stand still is preferable in the present invention.Although the aging time varies depending upon the aging method, a lapseof not less than 72 hours is necessary when the method of allowing thesolution to stand still is used singly. In case of the method of slowlystirring the solution, the aging time depends upon the stirringefficiency, and when the number of stirring times is 20 times/min, alapse of not less than about 16 hours is preferable. In case of themethod of applying ultrasonic wave to the solution, the aging timedepends upon the ultrasonic frequency, and when the ultrasonic frequencyis about 45 kHz, a lapse of not less than about 2 hours is preferable.

[0076] In the present invention, when the perfluorodicarboxylic acidfluoride (A) is mixed with cesium fluoride (CsF) in the aprotic polarsolvent with stirring, there is formed a polymerization initiator (B)represented by the following formula (II):

CsOCF₂—Rf—CF₂OCs  (II)

[0077] wherein Rf is a perfluoroalkylene group having 1 to 4 carbonatoms or a perfluoroalkylene group having 2 to 10 carbon atoms and anether bond.

[0078] In the later-described process for preparing a perfluoropolyetheraccording to the invention, a perfluoropolyether can be obtained bypolymerizing hexafluoropropylene oxide in the presence of theabove-mentioned polymerization initiator-containing solution, and in thepreparation of the polymerization initiator-containing solution, thereaction solution containing the polymerization initiator (B) is allowedto stand for not less than 72 hours at a temperature of 0 to 30° C.,whereby a bifunctional perfluoropolyether can be obtained with highselectivity and high degree of polymerization. If the lapse of time isless than 72 hours, selectivity of the resulting bifunctionalperfluoropolyether is lowered, and formation of a monofunctionalperfluoropolyether is increased.

[0079] That is to say, when the perfluorodicarboxylic acid fluoride (A)is mixed with cesium fluoride (CsF) in the aprotic polar solvent withstirring, the reaction is promoted in several hours to form apolymerization initiator (B), and then the activity of thepolymerization initiator-containing solution which contains thepolymerization initiator (B) changes with the lapse of time, wherebyselectivity of the bifunctional perfluoropolyether and degree ofpolymerization are enhanced.

[0080] This phenomenon is described below in more detail.

[0081] (1) The perfluorodicarboxylic acid fluoride (A) is mixed withcesium fluoride (CsF) with stirring, and after a lapse of a certainperiod of time, a peak of F of the —COF group at the end of the startingperfluorodicarboxylic acid fluoride (A) and a peak of F of the cesiumfluoride (CsF) are not observed by ¹⁹F-NMR, and the reaction of theperfluorodicarboxylic acid fluoride (A) with cesium fluoride proceedsalmost quantitatively.

[0082] (2) Each of FIGS. 1(a), 1(b), 1(c) and 1(d) shows a ¹⁹F-NMRspectrum of F atom of the —CF₂OCs group at the end of the polymerizationinitiator (B) and an integral value of the F atom. FIGS. 1(a), 1(b),1(c) and 1(d) show integral values of the F atom of the CF₂OCs group atthe end of the polymerization initiator (B) obtained after a lapse of 24hours, a lapse of 48 hours, a lapse of 96 hours and a lapse of onemonth, respectively. As is clear from FIG. 1, the central positions ofthe peaks in FIGS. 1(a), 1(b), 1(c) and 1(d) are the same as each other,and the compounds formed with the lapse of time are the same as eachother. That is to say, the polymerization initiator (B) is formed ineach case.

[0083] (3) As shown in FIG. 1, the peak of the F atom in case of a lapseof 24 hours (FIG. 1(a)) or a lapse of 48 hours (FIG. 1(b)) is broad andthe integral value is small, but the integral value of the F atom incase of a lapse of 96 hours (FIG. 1(c)) or a lapse of one month (FIG.1(d)) increases noticeably.

[0084] When the half band width of the peak of the F atom in the ¹⁹F-NMRspectral chart is measured, marked differences are found as shown inTable 1. TABLE 1 Lapse of time Half band width 24 hours 12 ppm  48 hours9 ppm 96 hours 3 ppm 30 days 2 ppm

[0085] That is to say, if the lapse of time exceeds 96 hours, the halfband width decreases noticeably.

[0086] In comparison between polymerization reaction ofhexafluoropropylene oxide using a polymerization initiator-containingsolution (a) obtained after a lapse of 24 hours and that using apolymerization initiator-containing solution (c) obtained after a lapseof 96 hours, the degree of polymerization and the selectivity of abifunctional perfluoropolyether are both low in case of the solutioncatalyst obtained after a lapse of 24 hours, while in case of thesolution catalyst obtained after a lapse of 96 hours a bifunctionalperfluoropolyether can be obtained with high degree of polymerizationand high selectivity.

[0087] The phenomenon that the activity of the resulting polymerizationinitiator-containing solution changes with the lapse of time ispresumably attributable to the following cause. That is, it is presumedthat, for not more than a certain period of time immediately aftersynthesis of the polymerization initiator (B), solvation between theaprotic polar solvent and the polymerization initiator (B) does notproceed sufficiently, and the polymerization initiator (B) is in anassociated cluster state. Hence, because of restraint due to theinteraction between molecules of the polymerization initiator (B), theintegral value of the F atom becomes broad, and the activity of thepolymerization initiator (B) is hardly exhibited. It is also presumedthat when a certain period of time passes after the reaction, salvationbetween the aprotic polar solvent and the polymerization initiator (B)proceeds to a considerable extent, and the association of thepolymerization initiator (B) is loosened to allow the polymerizationinitiator (B) to be present in the solvent. Hence, the activity of thepolymerization initiator (B) is apt to be exhibited.

[0088] After the mixing and stirring, the reaction solution obtained isallowed to stand at about room temperature, specifically a temperatureof 0 to 30° C., preferably 10 to 20° C.

[0089] If the temperature exceeds 30° C., the polymerizationinitiator-containing solution loses activity, and in the later-describedpreparation of a perfluoropolyether, the selectivity of the resultingbifunctional perfluoropolyether and the degree of polymerization aresometimes lowered. If the reaction temperature is lower than 0° C., therate of aging is lowered and the solution cannot be used practically.

[0090] The concentration of the polymerization initiator (B) in thepolymerization initiator-containing solution is preferably not less than4×10⁻⁴ mol/g, more preferably 4 to 20 mol/g, particularly preferably 4to 10 mol/g.

[0091] If the concentration is less than 4×10⁻⁴ mol/g, solidification ofthe solvent is liable to take place when polymerization of theperfluorodicarboxylic acid fluoride (A) is conducted at a lowtemperature for the purpose of preventing chain transfer. Accordingly,it is unfavorable to conduct reaction of the perfluorodicarboxylic acidfluoride (A) with cesium fluoride (CsF) in the solution of a lowconcentration in order to reduce association of the polymerizationinitiator (B), because the polymerization initiator-containing solutiondoes not function as a catalyst.

[0092] When the unreacted cesium fluoride is precipitated in thepolymerization initiator-containing solution obtained after a lapse of acertain period of time, it is possible to remove the cesium fluoride orto dispense the supernatant from the polymerization initiator-containingsolution.

Polymerization Initiator of the Second Invention and Process forPreparing Polymerization Initiator-containing Solution

[0093] In the present invention, the perfluorodicarboxylic acid fluoride(A′) represented by the formula (VI) is mixed with cesium fluoride (CsF)in the aprotic polar solvent with stirring, whereby there can beobtained a polymerization initiator-containing solution which contains apolymerization initiator (B′) represented by the following formula (IV):

(FOC)_(x)—Rf²—(CF₂OCs)_(y)  (IV)

[0094] wherein Rf² is perfluoroalkylene having 1 to 4 carbon atoms orperfluoroalkylene having 2 to 10 carbon atoms and an ether bond, and xand y are numbers satisfying the conditions of x+y=2 and 0.1<y<2.

[0095] In the later-described process for preparing a perfluoropolyetheraccording to the invention, a perfluoropolyether can be obtained bypolymerizing hexafluoropropylene oxide in the presence of theabove-mentioned polymerization initiator-containing solution, and in thepreparation of the polymerization initiator-containing solution, theperfluorodicarboxylic acid fluoride (A′) is allowed to react with CsF ina specific ratio, whereby a polymerization initiator (B′) for use in theinvention can be formed. By the use of the polymerizationinitiator-containing solution, a bifunctional perfluoropolyether can beobtained with excellent selectivity and excellent degree ofpolymerization.

[0096] The mixing ratio (CsF/perfluorodicarboxylic acid fluoride (A′),by mol) of the cesium fluoride to the perfluorodicarboxylic acidfluoride (A′) is preferably not less than 0.1 and less than 2, morepreferably 0.3 to 1.8, particularly preferably 0.5 to 1.8.

[0097] One of the reasons why the chain transfer takes place to form amonofunctional perfluoropolyether as a by-product is an action of freeCs⁺F⁻ in the reaction system, so that by decreasing the amount of thefree Cs⁺F⁻, a bifunctional perfluoropolyether can be obtained with highselectivity. Therefore, the ratio of CsF to FOCRf—COF needs to be lessthan 2, whereby occurrence of extra CsF can be avoided.

[0098] As the proportion of CsF becomes smaller, fluidity of thecatalyst at low temperatures can be kept better, and it becomes feasibleto enhance degree of polymerization and selectivity. To the contrary,when the proportion of CsF is too small, it becomes operationallydifficult to eliminate influences of water, HF or the like included fromthe starting materials, and hence lowering of selectivity and degree ofpolymerization is brought about.

[0099] More specifically, if the mixing ratio is not less than 2,selectivity of the resulting bifunctional perfluoropolyether becomesbad, and formation of a monofunctional perfluoropolyether is sometimesincreased.

[0100] If the mixing ratio is less than 0.1, the degree ofpolymerization and the selectivity of the bifunctional polyether aresometimes lowered because of chain transfer agents such as H₂O and HFincluded from the starting materials or included in the handlingprocess.

[0101] There is no specific limitation on the process for preparing thepolymerization initiator-containing solution which contains thepolymerization initiator (B′). For example, to CsF placed in a flaskequipped with a stirrer, a mixed solution of the perfluorodicarboxylicacid fluoride (A′) and the aprotic polar solvent is dropwise added withstirring the CsF in the flask. The temperature for the mixing is notspecifically limited and is usually room temperature.

[0102] Formation of the —CF₂OCs bond in the polymerization initiator(B′) can be confirmed by observing the —COF group at the molecular endof the perfluorodicarboxylic acid fluoride (A′) in the solution. Forexample, presence of the —COF group at the molecular end can beconfirmed by partly withdrawing a sample containing —COF from a reactionsolution that is being stirred and measuring an integral value of F atomof the —COF contained in the sample by means of ¹⁹F-NMR.

[0103] Specifically, the perfluorodicarboxylic acid fluoride (A′) ismixed with cesium fluoride (CsF) with stirring, and after a lapse of acertain period of time, the amounts of the —COF groups at the ends ofthe starting perfluorodicarboxylic acid fluoride (A′) are decreased, sothat a peak of F of the cesium fluoride is not observed by ¹⁹F-NMR, andthe reaction of the perfluorodicarboxylic acid fluoride (A′) with cesiumfluoride (CsF) proceeds almost quantitatively.

[0104] The concentration of the resulting polymerization initiator (B′)in the polymerization initiator-containing solution is preferably notless than 4×10⁻⁴ mol/g, more preferably 4×10⁻⁴ to 20×10⁻⁴ mol/g,particularly preferably 4×10⁻⁴ to 10×10⁻⁴ mol/g.

[0105] If the concentration is less than 4×10⁻⁴ mol/g, solidification ofthe solvent is liable to take place when polymerization of theperfluorodicarboxylic acid fluoride (A′) is conducted at a lowtemperature for the purpose of preventing chain transfer. Accordingly,it is unfavorable to conduct reaction of the perfluorodicarboxylic acidfluoride (A′) with cesium fluoride (CsF) in the solution of a lowconcentration in order to reduce association of the polymerizationinitiator (B′), because the polymerization initiator-containing solutiondoes not function as a catalyst.

[0106] Next, the process for preparing a perfluoropolyether according tothe invention is described.

Process for Preparing Perfluoropolyether

[0107] The process for preparing a perfluoropolyether according to thefirst or the second invention comprises polymerizing hexafluoropropyleneoxide (HFPO) in the presence of the polymerization initiator-containingsolution which can be obtained as described above. More specifically, itis preferable to add hexafluoropropylene oxide (HFPO) to thepolymerization initiator-containing solution which can be obtained byallowing the reaction solution to stand for a certain period of time asdescribed above, to conduct polymerization of HFPO.

[0108] In the first invention, various HFPO polymers (C) represented bythe following formula (VIII) can be obtained correspondingly to the typeof the polymerization initiator (B) represented by the formula (II), asindicated by the following reaction formula.

[0109] In the formula (VIII), Rf is a perfluoroalkylene group having 1to 4 carbon atoms or a perfluoroalkylene group having 2 to 10 carbonatoms and an ether bond, and a=b+c.

[0110] In the second invention, various HFPO polymers (C′) representedby the following formula (IX) can be obtained correspondingly to thetype of the polymerization initiator (B′) represented by the formula(IV), as indicated by the following reaction formula.

[0111] In the formula (IX), Rf² is a perfluoroalkylene group having 1 to4 carbon atoms or a perfluoroalkylene group having 2 to 10 carbon atomsand an ether bond, and a=b+c.

[0112] In the first and the second inventions, the amount of the HFPO tobe fed is properly determined, and the amount thereof is desired to bein the range of preferably 10 to 400 mol, more preferably 20 to 200 mol,based on 1 mol of the polymerization initiator (B) or (B′) contained inthe polymerization initiator-containing solution. The HFPO may be fed inany of gas state and liquid state.

[0113] The temperature of the mixed solution of the polymerizationinitiator-containing solution and HFPO is desired to be in the range of−35 to −40° C., preferably −33 to −38° C. It is preferable to mix themunder the conditions by which the temperature is kept constant at atemperature in the above range. Although the feeding time is notspecifically limited, it is preferably in the range of 3 to 120 hours.

[0114] The reaction temperature after the polymerizationinitiator-containing solution is mixed with HFPO is desired to be in therange of −30 to −50° C., preferably −35 to −40° C.

[0115] After the polymerization is completed, the internal temperatureis maintained at a temperature of −40 to −30° C., preferably −35 to −40°C., and aging is conducted for about 1 to 10 hours, followed by raisingthe temperature. Thus, a perfluoropolyether represented by the formula(VIII) or (IX) can be obtained.

[0116] In the polymerization of HFPO in the presence of thepolymerization initiator (B) or (B′), hexafluoropropylene may be furtherfed simultaneously with feeding of the HFPO. The hexafluoropropylene isdesired to be fed in an amount of preferably 20 to 100% by weight, morepreferably 30 to 90% by weight, based on the amount of thehexafluoropropylene oxide.

Effect of the Invention

[0117] The polymerization initiator-containing solution of the inventionis a solution catalyst which serves as a polymerization catalyst, can bein a liquid state even at a low temperature during the polymerizationreaction, can be homogeneously dispersed in the polymerization reactionsystem and exhibits low chain transfer property and high activity. Theprocess for preparing a perfluoropolyether according to the inventionuses a special polymerization initiator-containing solution as apolymerization catalyst, and hence a bifunctional perfluoropolyether canbe obtained with high degree of polymerization and high selectivity.Moreover, the polymerization initiator-containing solution is highlyactive, and hence, even if a small amount of a chain transfer substanceis contained in the solution, a bifunctional perfluoropolyether can beobtained with high degree of polymerization and high selectivity.

EXAMPLE

[0118] The present invention is further described with reference to thefollowing examples, but it should be construed that the invention is inno way limited to those examples.

[0119] The first invention is now described with reference to thefollowing examples.

Catalyst Preparation Example A1

[0120] In a thoroughly dried 500 ml flask equipped with a droppingfunnel, a condenser, a gas feed pipe and a stirrer, 9 g (59.2 mmol) ofCsF having been calcined at 300° C. and then pulverized was placed.Then, 31.3 g of tetraglyme and 10.5 g (24.64 mmol) ofF—CO—CCF₃F—OCF₂CF₂O—CFCF₃—CO—F were added at room temperature (20° C.)through the dropping funnel. After the dropwise addition was completed,the mixture was stirred at a temperature of 30° C. Then, stirring wascontinued, while presence of a —COF group at the end of the startingFOC—CF(CF₃)—OCF₂CF₂O—CF(CF₃)—COF in the reaction solution was confirmedby ¹⁹F-NMR. When the end —COF group disappeared, stirring was stopped.The reaction solution was allowed to stand still for one night (about 12hours) at room temperature (20° C.), and then the unreacted CsF wasremoved. The reaction solution was further allowed to stand still for(a) 24 hours, (b) 48 hours, (c) 96 hours and (d) 30 days in total fromthe disappearance of the —COF group, to obtain catalyst solutions (a),(b), (c) and (d). From ¹⁹F-NMR and gas chromatography, it was confirmedthat the reaction proceeded almost quantitatively. Calculation of theconcentration of the polymerization initiatorCsO—CF₂—CF(CF₃)—OCF₂CF₂O—CF(CF₃)—CF₂—OCs in the catalyst solutionresulted in 5×10⁻⁴ mol/l.

[0121] In FIGS. 1(a), 1(b), 1(c) and 1(d), ¹⁹F-NMR spectra and integralvalues of F atom of the end —CF₂—OCs of the products contained in thecatalyst solutions (a), (b), (c) and (d) obtained by allowing thereaction solution to stand still for 24 hours, 48 hours, 96 hours and 30days, respectively, are shown.

Catalyst Preparation Example A2

[0122] Mixing of the starting materials was carried out in the samemanner as in Catalyst Preparation Example A1, except that 4.2 g (9.86mmol) of F—CO—CCF₃F—OCF₂CF₂O—CFCF₃—CO—F was used in place of 10.5 g(24.64 mmol) of F—CO—CCF₃F—OCF₂CF₂O—CFCF₃—CO—F. When the end COF groupdisappeared, stirring was stopped similarly to Catalyst PreparationExample A1. The reaction solution was allowed to stand still for onenight (about 12 hours) at room temperature (20° C.), and then theunreacted CsF was removed. The reaction solution was further allowed tostand still for 24 hours in total from the disappearance of the —COFgroup, to obtain a catalyst solution (e). From ¹⁹F-NMR and gaschromatography, it was confirmed that the reaction proceeded almostquantitatively. Calculation of the concentration of the polymerizationinitiator CsO—CF₂—CF(CF₃)—OCF₂CF₂O—CF(CF₃)—CF₂—OCs in the catalystsolution resulted in 2×10⁻⁴ mol/l.

Example A1

[0123] In a thoroughly dried 500 ml flask, 44.4 g (5×10⁻⁴ mol/g) of thecatalyst solution (c) prepared by allowing the reaction solution tostand still for 96 hours in Catalyst Preparation Example A1 was placed.Then, 12 g of hexafluoropropylene (HFP) was fed at room temperature,followed by stirring for 50 minutes. The mixed solution obtained wascooled to −38° C., and thereto was further added 18 g of HFP. To thesolution, a mixed gas of 147 g of hexafluoropropylene oxide (HFPO) and89 g of HFP was fed at a temperature of −38 to −32° C. over a period of24 hours. After feeding of the mixed gas of HFPO and HFP was completed,stirring was further performed for 4 hours at the same temperature, thenthe temperature of the system was raised, and the unreacted HFP wasrecovered.

[0124] To the reaction solution, 500 g of methanol and 70 g ofCF₂ClCFCl₂ were added, and they were stirred for 30 minutes. From theseparated phases, the lower layer was dispensed, and the volatilecomponent was distilled off at 120° C. and 1 mmHg to obtain 148 g of amixed solution of a bifunctional perfluoropolyether represented by thefollowing formula (A) and a monofunctional perfluoropolyetherrepresented by the following formula (B).

[0125] The results of ¹⁹F-NMR spectrometry of the mixed solution areshown in Table 2. TABLE 2 F for integral Chemical shift Integral valuevalue *1 −69.5 ppm m = 5.43  —OCFCF₂— −56.8 ppm k = 0.26  —CF—CO— −54.8ppm x = 0.037 CF₃CF₂CF₂O— −5 to −8 ppm n = 30.7  CF₃—, —OCF₂CF—

[0126] Using the above results, the following calculations were made,and as a result, the mean degree of polymerization was 39 and theselectivity (A)/(B) was 87/13.

[0127] Mean degree of polymerization: 2 m/(k+0.5×)=39

[0128] Selectivity: (100(k−0.5×)/(k+0.5×))/(100×/(k+0.5×))=87/13

Comparative Example A1

[0129] In a thoroughly dried 500 ml flask, 13.0 g (2×10⁻⁴ mol/g) of thecatalyst solution (e) prepared by allowing the reaction solution tostand still for 24 hours in Catalyst Preparation Example A2 was placed,followed by stirring at −35° C. for 15 minutes. Thereafter, 4 g ofhexafluoropropylene (HFP) was fed, followed by stirring for about 60minutes. The mixed solution obtained was cooled to −38° C., and to thesolution, a mixed gas of 108 g of hexafluoropropylene oxide (HFEPO) and54 g of HFP was fed at a temperature of −38 to −32° C. After about 30minutes from beginning of feeding the mixed gas, the reaction solutionsolidified, and a perfluoropolyether was not obtained at all.

Comparative Example A2

[0130] In a thoroughly dried 500 ml flask, 20.0 g (5×10⁻⁴ mol/g) of thecatalyst solution (a) prepared by allowing the reaction solution tostand still for 24 hours in Catalyst Preparation Example A1 was placed,then cooled to −35° C. and stirred for 1 hour. Thereafter, 5 g ofhexafluoropropylene (HFP) was fed, followed by stirring for 20 minutesat the same temperature. To the solution, 100.8 g of a mixed gas of 85.7g of hexafluoropropylene oxide (HFPO) and 15.1 g of HFP was fed at atemperature of −38 to −32° C. over a period of 13 hours. After feedingof the mixed gas of HFPO and HFP was completed, stirring was furtherperformed for 4 hours at the same temperature (−38 to −32° C.). Afterthe reaction was completed, the cooled unreacted gas was distilled offunder reduced pressure. Thereafter, to the reaction solution was added100 g of methanol, followed by stirring for 10 minutes. From theseparated phases, the lower layer was dispensed, and the volatilecomponent was distilled off at 120° C. and 1 mmhg to obtain 42 g of amixed solution of a bifunctional perfluoropolyether represented by theaforesaid formula (A) and a monofunctional perfluoropolyetherrepresented by the aforesaid formula (B).

[0131] The results of ¹⁹F-NMR spectrometry of the mixed solution areshown in Table 3. TABLE 3 F for integral Chemical shift Integral valuevalue *1 −69.8 ppm m = 35.56 —OCFCF₂— −56.8 ppm k = 4.94  —CF—CO— −54.8ppm x = 3.20  CF₃CF₂CF₂O— −5 to −8 ppm n = 214.3 CF₃—, —OCF₂CF

[0132] Using the above results, the following calculations were made,and as a result, the mean degree of polymerization was 11 and theselectivity (A)/(B) was 51/49.

[0133] Mean degree of polymerization: 2 m/(k+0.5×)=11

[0134] Selectivity: (100(k−0.5×)/(k+0.5×))/(100×/(k+0.5×))=51/49

[0135] Next, the second invention is described with reference to thefollowing examples.

Catalyst Preparation Example B1

[0136] Preparation of Catalyst Solution (a′)

[0137] In a thoroughly dried 500 ml flask equipped with a droppingfunnel, a condenser, a gas feed pipe and a stirrer, 4.8 g (31.6 mmol) ofCsF having been calcined at 300° C. for 2 hours and then pulverized wasplaced. In the flask, the CsF was vacuum dried at 220° C. and 1 mmHg for1 hour. Then, 45 g of tetraglyme and 13.5 g (31.6 mmol) of F—CO—C (CF₃)F—OCF₂CF₂O—CF (CF₃)—COF were added at room temperature (20° C.) throughthe dropping funnel. After the dropwise addition was completed, themixture was stirred at a temperature of 30° C. Then, stirring wascontinued, while presence of a —COF group at the end of the startingFOC—CF(CF₃)—OCF₂CF₂O—CF(CF₃)—COF in the reaction solution was confirmedby ¹⁹F-NMR. When the amounts of the end —COF groups were reduced tohalf, stirring was stopped. The reaction solution was allowed to standstill for one night (about 12 hours) at room temperature (20° C.), andthen the unreacted CsF was removed. Calculation of the concentration ofthe polymerization initiator CsO—CF₂—CF(CF₃)—OCF₂CF₂O—CF(CF₃)—CFO in thecatalyst solution (a′) resulted in 5×10⁻⁴ mol/g, and calculation of themolar ratio (FOCRfCOF:CsF) between FOCRfCOF and CsF resulted in 1:1.

Catalyst Preparation Example B2

[0138] Preparation of Catalyst Solution (b′)

[0139] Mixing of the starting materials was carried out in the samemanner as in Catalyst Preparation Example B1, except thatF—CO—CCF₃F—OCF₂CF₂O—CFCF₃—CO—F was used in an amount of 14.9 g (34.98mmol) and CsF was used in an amount of 7.1 g (46.71 mmol). When theamounts of the end —COF groups were reduced, stirring was stoppedsimilarly to Catalyst Preparation Example B1. The reaction solution wasallowed to stand still for one night (about 12 hours) at roomtemperature (20°C.), and then the unreacted CsF was removed to obtain acatalyst solution (b′). Calculation of the concentration of thepolymerization initiator(OCF)_(0.5)CF(CF₃)—OCF₂CF₂O—CF(CF₃)—(CF₂—OCs)_(1.5) resulted in 5×10⁴mol/g, and calculation of the molar ratio (FOCRfCOF:CsF) betweenFOCRfCOF and CsF resulted in 1:1.5.

Catalyst Preparation Example B3

[0140] Preparation of Catalyst Solution (c′)

[0141] A catalyst solution (c′) was prepared in the same manner as inCatalyst Preparation Example B1, except that CsF was used in an amountof 6.8 g (43.3 mmol), FOCCF(CF₃)OCF₂CF₂OCF(CF₃)COF was used in an amountof 10.5 g (26.64 mmol), and tetraglyme was used in an amount of 31.3 g.

[0142] Calculation of the concentration of the polymerization initiator(FOC)_(0.25)CF(CF₃)OCF₂CF₂OCF(CF₃)—(CF₂OCs)_(1.75) resulted in 5×10⁻⁴mol/g, and calculation of the molar ratio (FOCRfCOF:CsF) betweenFOCRfCOF and CsF resulted in 1:1.75.

Catalyst Preparation Example B4

[0143] Preparation of Catalyst Solution (d′)

[0144] A catalyst solution (d′) was prepared in the same manner as inCatalyst Preparation Example B1, except that CsF was used in an amountof 2.9 g (19.0 mmol).

[0145] Calculation of the concentration of the polymerization initiator(FOC)_(1.4)—CF(CF₃)OCF₂CF₂OCF(CF₃)—(CF₂—OCs)_(0.6) resulted in 5×10⁻⁴mol/g, and calculation of the molar ratio (FOCRfCOF:CsF) betweenFOCRfCOF and CsF resulted in 1:0.6.

Catalyst Preparation Example B5

[0146] Preparation of Catalyst Solution (e′)

[0147] In a thoroughly dried 500 ml flask equipped with a droppingfunnel, a condenser, a gas feed pipe and a stirrer, 9 g (59.2 mmol) ofCsF having been calcined at 300° C. for 2 hours and then pulverized wasplaced. In the flask, the CsF was vacuum dried at 220° C. and 1 mmHg for1 hour. Then, 31.3 g of tetraglyme and 4.2 g (19.86 mmol) ofF—CO—C(CF₃)F—OCF₂CF₂O—CF(CF₃)—CO—F were added at room temperature (20°C.) through the dropping funnel. After the dropwise addition wascompleted, the mixture was stirred at a temperature of 30° C. Then,stirring was continued, while presence of a —COF group at the end of thestarting FOC—CF(CF₃)—OCF₂CF₂O—CF(CF₃)—COF in the reaction solution wasconfirmed by ¹⁹F-NMR. When the end —COF group disappeared, stirring wasstopped. The reaction solution was allowed to stand still for one night(about 12 hours) at room temperature (20° C.), and then the unreactedCsF was removed. The reaction solution was further allowed to standstill for 24 hours in total from the disappearance of the end —COFgroup, to obtain a catalyst solution (e′). Calculation of theconcentration of the polymerization initiatorCsO—CF₂—CF(CF₃)—OCF₂CF₂O—CF(CF₃)—CF₂—OCs in the catalyst solution (e′)resulted in 2×10⁻⁴ mol/g, and calculation of the molar ratio(FOCRfCOF:CsF) between FOCRfCOF and CsF resulted in 1:6.

Catalyst Preparation Example B6

[0148] Preparation of Catalyst Solution (f)

[0149] In a thoroughly dried 500 ml flask equipped with a droppingfunnel, a condenser, a gas feed pipe and a stirrer, 9 g (59.2 mmol) ofCsF having been calcined at 300° C. for 2 hours and then pulverized wasplaced. In the flask, the CsF was vacuum dried at 220° C. and 1 mmHg for1 hour. Then, 31.3 g of tetraglyme and 10.5 g (24.64 mmol) of F—CO—C(CF₃) F—OCF₂CF₂O—CF (CF₃)—CO—F were added at room temperature (20° C.)through the dropping funnel. After the dropwise addition was completed,the mixture was stirred at a temperature of 30° C. Then, stirring wascontinued, while presence of a —COF group at the end of the startingFOC—CF (CF₃)—OCF₂CF₂O —CF(CF₃)—COF in the reaction solution wasconfirmed by ¹⁹F-NMR. When the end —COF group disappeared, stirring wasstopped. The reaction solution was allowed to stand still for one night(about 12 hours) at room temperature (20° C.), and then the unreactedCsF was removed. The reaction solution was further allowed to standstill for 24 hours in total from the disappearance of the —COF group, toobtain a catalyst solution (f). Calculation of the concentration of thepolymerization initiator CsO—CF₂—CF(CF₃)—OCF₂CF₂O—CF(CF₃)—CF₂—OCs in thecatalyst solution (f) resulted in 5×10⁻⁴ mol/g, and calculation of themolar ratio (FOCRfCOF:CsF) between FOCRfCOF and CsF resulted in 1:2.4.

Example B1

[0150] In a thoroughly dried 500 ml flask, 43.5 g (5×10⁻⁴ mol/g) of thecatalyst solution (a′) prepared in Catalyst Preparation Example B1 wasplaced. Thereafter, 12 g of hexafluoropropylene (HFP) was fed at roomtemperature, followed by stirring for 50 minutes. The mixed solutionobtained was cooled to −35° C., and thereto was further added 12 g ofHFP. Into the solution, a mixed gas of 135 g of hexafluoropropyleneoxide (HFPO) and 87 g of HFP was injected at a temperature of —35 to−32° C. over a period of 17 hours. After feeding of the mixed gas ofHFPO and HFP was completed, stirring was further performed for 1 hour atthe same temperature, then the temperature of the system was raised, andthe unreacted HFP was recovered.

[0151] To the reaction solution, 300 g of methanol and 88 g ofCF₂ClCFCl₂ were added, and they were stirred for 30 minutes. From theseparated phases, the lower layer was dispensed, and the volatilecomponent was distilled off at 120° C. and 1 mmHg to obtain 115 g of amixed solution of a bifunctional perfluoropolyether represented by thefollowing formula (A) and a monofunctional perfluoropolyetherrepresented by the following formula (B).

[0152] The results of ¹⁹F-NMR spectrometry of the mixed solution areshown in Table 4. TABLE 4 F for integral Chemical shift Integral valuevalue −69.8 ppm m = 29.854 —OCFCF₂— −56.8 ppm k = 1.502  —CF—CO— −54.8ppm x = 0.075  CF₃CF₂CF₂O— −5 to −8 ppm n = 163.05 CF₃—, OCF₂CF—

[0153] Using the above results, the following calculations were made,and as a result, the mean degree of polymerization was 38.8 and theselectivity (A)/(B) was 95/5.

[0154] Mean degree of polymerization: 2 m/(k+0.5×)=38.8

[0155] Selectivity: (100(k−0.5×)/(k+0.5×))/(100×/(k+0.5×))=95/5

Example B2

[0156] In a thoroughly dried 500 ml flask, 38.8 g (5×10⁻⁴ mol/g) of thecatalyst solution (b′) prepared in Catalyst Preparation Example B2 wasplaced. Thereafter, 10 g of hexafluoropropylene (HFP) was fed at roomtemperature, followed by stirring for 40 minutes. The mixed solutionobtained was cooled to −35° C., and thereto was further added 11 g ofHFP. Into the solution, a mixed gas of 114 g of hexafluoropropyleneoxide (HFPO) and 65 g of HFP was injected at a temperature of −35 to−32° C. over a period of 20 hours. After feeding of the mixed gas ofHFPO and HFP was completed, stirring was further performed for 1 hour atthe same temperature, then the temperature of the system was raised, andthe unreacted HFP was recovered.

[0157] To the reaction solution, 300 g of methanol and 88 g ofCF₂ClCFCl₂ were added, and they were stirred for 30 minutes. From theseparated phases, the lower layer was dispensed, and the volatilecomponent was distilled off at 120° C. and 1 mmHg to obtain 122 g of amixed solution of a bifunctional perfluoropolyether represented by thefollowing formula (A) and a monofunctional perfluoropolyetherrepresented by the following formula (B).

[0158] The results of ¹⁹F-NMR spectrometry of the mixed solution-areshown in Table 5. TABLE 5 F for integral Chemical shift Integral valuevalue −69.8 ppm m = 9.66  —OCFCF₂— −56.8 ppm k = 0.45  —CF—CO— −54.8 ppmx = 0.052 CF₃CF₂CF₂O— −5 to −8 ppm n = 55.33 CF₃—, OCF₂CF—

[0159] Using the above results, the following calculations were made,and as a result, the mean degree of polymerization was 40.7 and theselectivity (A)/(B) was 89/11.

[0160] Mean degree of polymerization: 2 m/(k+0.5×)=40.7

[0161] Selectivity:(100(k−0.5×)/(k+0.5×))/(100×/(k+0.5×))=89/11

Example B3

[0162] In a thoroughly dried 500 ml flask, 27.7 g (5×10⁻⁴ mol/g) of thecatalyst solution (c′) prepared in Catalyst Preparation Example B3 wasplaced. Thereafter, 12 g of hexafluoropropylene (HFP) was fed at roomtemperature, followed by stirring for 60 minutes. The mixed solutionobtained was cooled to −35° C., and thereto was further added 12 g ofHFP. Into the solution, a mixed gas of 92 g of hexafluoropropylene oxide(HFPO) and 32 g of HFP was injected at a temperature of −35 to −32° C.over a period of 14 hours. After feeding of the mixed gas of HFPO andHFP was completed, stirring was further performed for 1 hour at the sametemperature, then the temperature of the system was raised, and theunreacted HFP was recovered.

[0163] To the reaction solution, 300 g of methanol and 70 g ofCF₂ClCFCl₂ were added, and they were stirred for 30 minutes. From theseparated phases, the lower layer was dispensed, and the volatilecomponent was distilled off at 120° C. and 1 mmHg to obtain 95 g of amixed solution of a bifunctional perfluoropolyether represented by thefollowing formula (A) and a monofunctional perfluoropolyetherrepresented by the following formula (B).

[0164] The results of ¹⁹F-NMR spectrometry of the mixed solution areshown in Table 6. TABLE 6 F for integral Chemical shift Integral valuevalue −69.8 ppm m = 9.81 —OCFCF₂— −56.8 ppm k = 0.44 —CF—CO— −54.8 ppm x= 0.04 CF₃CF₂CF₂O— −5 to −8 ppm  n = 52.59 CF₃—, —OCF₂CF—

[0165] Using the above results, the following calculations were made,and as a result, the mean degree of polymerization was 42.7 and theselectivity (A)/(B) was 91/9.

[0166] Mean degree of polymerization: 2 m/(k+0.5×)=42.7

[0167] Selectivity: (100(k−0.5×)/(k+0.5×))/(100×/(k+0.5×))=91/9

Example B4

[0168] In a thoroughly dried 500 ml flask, 42.5g (5×10⁻⁴ mol/g) of thecatalyst solution (d′) prepared in Catalyst Preparation Example B4 wasplaced. Thereafter, 12 g of hexafluoropropylene (HFP) was fed at roomtemperature, followed by stirring for 60 minutes. The mixed solutionobtained was coo led to −35° C., and thereto was further added 12 g ofHFP. Into the solution, a mixed gas of 126 g of hexafluoropropyleneoxide (HFPO) and 91 g of HFP was injected at a temperature of −35 to−32° C. over a period of 26 hours. After feeding of the mixed gas ofHFPO and HFP was completed, stirring was further performed for 1 hour atthe same temperature, then the temperature of the system was raised, andthe unreacted HFP was recovered.

[0169] To the reaction solution, 300 g of methanol and 88 g ofCF₂ClCFCl₂ were added, and they were stirred for 30 minutes. From theseparated phases, the lower layer was dispensed, and the volatilecomponent was distilled off at 120° C. and 1 mmHg to obtain 97 g of amixed solution of a bifunctional perfluoropolyether represented by thefollowing formula (A) and a monofunctional perfluoropolyetherrepresented by the following formula (B).

[0170] The results of ¹⁹F-NMR spectrometry of the mixed solution areshown in Table 7. TABLE 7 F for integral Chemical shift Integral valuevalue −69.8 ppm m = 19.62  —OCFCF₂— 56.8 ppm k = 0.91  —CF—CO— −54.8 ppmx = 0.07  CF₃CF₂CF₂O— −5 to −8 ppm n = 105.18 CF₃—, OCF₂CF

[0171] Using the above results, the following calculations were made,and as a result, the mean degree of polymerization was 41.5 and theselectivity (A)/(B) was 92/8.

[0172] Mean degree of polymerization: 2 m/(k+0.5×)=41.5

[0173] Selectivity:(100(k−0.5—)/(k+0.5×))/(100×/(k+0.5×))=92/8

Comparative Example B1

[0174] In a thoroughly dried 500 ml flask, 13.0 g (2×10⁻⁴ mol/g) of thecatalyst solution (e′) prepared in Catalyst Preparation Example B5 wasplaced, followed by stirring at −35° C. for 15 minutes. Then, 4 g ofhexafluoropropylene (HFF) was fed, followed by stirring for about 60minutes. The mixed solution obtained was cooled to −38° C., and to thesolution, a mixed gas of 108 g of hexafluoropropylene oxide (HFPO) and54 g of HFP was fed at a temperature of −38 to −32° C. After about 30minutes from beginning of feeding the mixed gas, the reaction solutionsolidified, and a perfluoropolyether was not obtained at all.

Comparative Example B2

[0175] In a thoroughly dried 500 ml flask, 20.0 g (5×10⁻⁴ mol/g) of thecatalyst solution (f) prepared in Catalyst Preparation Example B6 wasplaced, then cooled to −35° C. and stirred for 1 hour. Thereafter, 5 gof hexafluoropropylene (HFP) was fed, followed by stirring for 20minutes at the same temperature. To the solution, 100.8 g of a mixed gasof 85.7 g of hexafluoropropylene oxide (HFPO) and 15.1 g of HFP was fedat a temperature of −38 to −32° C. over a period of 13 hours. Afterfeeding of the mixed gas of HFPO and HFP was completed, stirring wasfurther performed for 4 hours at the same temperature (−38 to −32° C.).After the reaction was completed, the cooled unreacted gas was distilledoff under reduced pressure. Thereafter, to the reaction solution wasadded 100 g of methanol, followed by stirring for 10 minutes. From theseparated phases, the lower layer was dispensed, and the volatilecomponent was distilled off at 120° C. and 1 mmHg to obtain 42 g of amixed solution of a bifunctional perfluoropolyether represented by theaforesaid formula (A) and a monofunctional perfluoropolyetherrepresented by the aforesaid formula (B).

[0176] The results of ¹⁹F-NMR spectrometry of the mixed solution areshown in Table 8. TABLE 8 F for integral Chemical shift Integral valuevalue −69.8 ppm m = 35.56 —OCFCF₂— −56.8 ppm k = 4.94  —CF—CO— −54.8 ppmx = 3.20  CF₃CF₂CF₂O— −5 to −8 ppm n = 214.3 CF₃—, OCF₂CF—

[0177] Using the above results, the following calculations were made,and as a result, the mean degree of polymerization was 11 and theselectivity (A)/(B) was 51/49.

[0178] Mean degree of polymerization: 2 m/(k+0.5×)=11

[0179] Selectivity:(100(k−0.5×)/(k+0.5×))/(100×/(k+0.5×))=51/49

What is claimed is:
 1. A polymerization initiator-containing solutioncapable of being obtained by mixing a perfluorodicarboxylic acidfluoride (A) represented by the following formula (I) with CsF in anaprotic polar solvent with stirring to conduct reaction and thereby forma polymerization initiator (B) and then allowing the reaction solutionto stand for not less than 72 hours at a temperature of 0 to 30° C.;FOC—Rf—COF  (I) wherein Rf is a perfluoroalkylene group having 1 to 4carbon atoms or a perfluoroalkylene group having 2 to 10 carbon atomsand an ether bond.
 2. A process for preparing a polymerizationinitiator-containing solution, comprising mixing a perfluorodicarboxylicacid fluoride (A) represented by the following formula (I) with CsF inan aprotic polar solvent with stirring to conduct reaction and therebyform a polymerization initiator (B) and then allowing the reactionsolution to stand for not less than 72 hours at a temperature of 0 to30° C.; FOC—Rf—COF  (I) wherein Rf is a perfluoroalkylene group having 1to 4 carbon atoms or a perfluoroalkylene group having 2 to 10 carbonatoms and an ether bond.
 3. A process for preparing aperfluoropolyether, comprising polymerizing hexafluoropropylene oxide inthe presence of the polymerization initiator-containing solution ofclaim 1 .
 4. The process for preparing a perfluoropolyether as claimedin claim 3 , wherein the polymerization initiator (B) contained in thepolymerization initiator-containing solution is a compound representedby the following formula (II): CsOCF₂—Rf—CF₂OCs  (II) wherein Rf is aperfluoroalkylene group having 1 to 4 carbon atoms or aperfluoroalkylene group having 2 to 10 carbon atoms and an ether bond.5. The process for preparing a perfluoropolyether as claimed in claim 3or 4, wherein the concentration of the polymerization initiator (B) inthe polymerization initiator-containing solution is not less than 4×10⁻⁴mol/g.
 6. The process for preparing a perfluoropolyether as claimed inany one of claims 3 to 5, wherein the perfluorodicarboxylic acidfluoride (A) is represented by the following formula (III):

wherein Rf¹ is a perfluoroalkylene group having 2 to 4 carbon atoms. 7.A process for preparing a perfluoropolyether, comprising polymerizinghexafluoropropylene oxide in the presence of a polymerizationinitiator-containing solution which comprises a polymerization initiator(B′) represented by the following formula (IV) and an aprotic polarsolvent; (FOC)_(x)—Rf²—(CF₂OCs)_(y)  (IV) wherein Rf² isperfluoroalkylene having 1 to 4 carbon atoms or perfluoroalkylene having2 to 10 carbon atoms and an ether bond, and x and y are numberssatisfying the conditions of x+y=2 and 0.1<y<2.
 8. The process forpreparing a perfluoropolyether as claimed in claim 7 , wherein Rf² inthe formula (IV) is represented by the following formula (V):

wherein Rf³ is perfluoroalkylene having 2 to 6 carbon atoms.
 9. Theprocess for preparing a perfluoropolyether as claimed in any one ofclaims 3 to 8 , wherein polymerization of the hexafluoropropylene oxideis carried out at a temperature of not higher than −30° C.
 10. Theprocess for preparing a perfluoropolyether as claimed in any one ofclaims 7 to 9 , wherein the concentration of the polymerizationinitiator (B′) in the polymerization initiator-containing solution isnot less than 4×10⁻⁴ mol/g.
 11. The process for preparing aperfluoropolyether as claimed in any one of claims 3 to 10 , wherein, inthe polymerization of the hexafluoropropylene oxide, hexafluoropropyleneis further used in combination in an amount of 20 to 50% by weight basedon the amount of the hexafluoropropylene oxide.
 12. The process forpreparing a perfluoropolyether as claimed in any one of claims 7 to 11,wherein the polymerization initiator (B′) is a compound obtained byallowing a perfluorodicarboxylic acid fluoride (A′) represented by thefollowing formula (VI) to react with CsF in an aprotic polar solvent;FOC—Rf⁴—COF  (VI) wherein Rf⁴ is a perfluoroalkylene group having 1 to 4carbon atoms or a perfluoroalkylene group having 2 to 10 carbon atomsand an ether bond.
 13. The process for preparing a perfluoropolyether asclaimed in claim 12 , wherein the perfluorodicarboxylic acid fluoride(A′) is represented by the following formula (VII):

wherein Rf⁵ is a perfluoroalkylene group having 2 to 4 carbon atoms. 14.The process for preparing a perfluoropolyether as claimed in claim 12 or13, wherein the molar ratio (CsF/perfluorodicarboxylic acid fluoride(A′)) of the CsF to the perfluorodicarboxylic acid fluoride (A′) used isnot less than 0.1 and less than
 2. 15. The process for preparing aperfluoropolyether as claimed in any one of claims 3 to 14 , wherein theaprotic polar solvent is diglyme, triglyme, tetraglyme or sulfolane.